The invention relates to a motor vehicle having a fuel cell, an air compressor for providing intake air under pressure to the fuel cell, and an electric drive motor for driving the motor vehicle, which electric drive motor can be supplied with electric current by the fuel cell for this purpose. Furthermore, the invention relates to a method for operating a fuel cell of this type in a motor vehicle.
Fuel cell systems, in particular those of hybrid motor vehicles, have an air compressor or compressed air deliverer for delivering compressed air, by way of which sufficient oxygen for the operation of the associated fuel cell is provided from the surroundings of the fuel cell system. To this end, the air compressor is regulated during operation of the fuel cell system in such a way that it supplies the correct pressure and mass flow of compressed air for the respective operating state of the fuel cell. To this end, the air compressor is driven by a separate electric compressor drive motor. The drive power of the latter can be controlled separately in a corresponding manner in the case of load jumps in the fuel cell.
According to the invention, a motor vehicle having a fuel cell, an air compressor for providing intake air under pressure to or in the fuel cell, and an electric drive motor for driving the motor vehicle is provided. Here, the drive motor can be supplied with electric current by the fuel cell. Moreover, the air compressor of the fuel cell is driven by the drive motor, as it were, in the reverse direction. This driving of the air compressor preferably classically takes place in a mechanical way. To this end, the drive motor is particularly preferably connected to the air compressor by way of a torque-transmitting coupling. The said coupling can advantageously be of coupleable design. In order to improve the overall degree of efficiency, the air compressor can then be decoupled completely from the drive motor in certain operating states.
An otherwise necessary, separate drive for the air compressor is dispensed with by way of the coupling according to the invention of the drive motor to the air compressor of an associated fuel cell. Furthermore, it is possible by way of the drive motor to use the latter in overrun or generator operation during braking operations and to conduct said mechanical overrun power directly into the air compressor. An otherwise necessary conversion into electric current at the drive motor and conversion back into mechanical rotational power at the air compressor are therefore dispensed with.
Decoupling of the air compressor from the drive motor can be advantageous, in particular, when only a small power output is called up at the fuel cell, but the drive motor can provide a greater recuperation power output on account of overrun operation. Said recuperation power output can then be utilized completely in generator operation for electrical energy for buffer-storing in associated batteries.
Furthermore, the coupling is preferably designed with a switchable gear mechanism which can be switched, in particular, into two stages. A gear mechanism of this type can be regulated to two rotational speeds at the gear mechanism output. In this way, two performance ranges can be predefined for the connected air compressor, within which performance ranges said air compressor can deliver its compressed air into a compressed air store. The compressed air can then be provided to the fuel cell as intake air as required and in a finely metered manner from the pressure store device which is preferably designed in the form of a compressed air tank.
Moreover, the gear mechanism can preferably be coupled in a torque-transmitting manner to a drive axle of the motor vehicle. A gear mechanism of this type assumes several functions by serving both to drive an air compressor of the fuel cell and an output axle of the motor vehicle. All the required mechanical drives are therefore present in a combined manner in the gear mechanism. Here, correlations in the case of the required rotational speeds at the individual consumers can advantageously be utilized to keep the complexity of the gear mechanism low.
Furthermore, the gear mechanism according to the invention can preferably be coupled in a torque-transmitting manner to an air expander for discharging waste air under pressure from the fuel cell. An air expander which can be coupled in this way, in particular selectively, provides recuperation power from the waste air which is discharged from the fuel cell under residual pressure. It therefore utilizes the residual enthalpy of said waste air, in order to convert it into mechanical rotational energy and to utilize it for driving the air compressor and/or the drive axle.
The invention is correspondingly also directed to a method for operating a fuel cell in a motor vehicle, in which method intake air is provided under pressure to the fuel cell by way of an air compressor and the motor vehicle is driven by way of an electric drive motor, the air compressor being driven by the drive motor. The drive of the air compressor preferably takes place purely mechanically. Here, the drive motor is preferably connected to the air compressor by way of a torque-transmitting coupling. Said coupling is preferably effected in a coupleable manner. Furthermore, the coupling is preferably designed with a switchable gear mechanism which is switched, in particular, into two stages. Moreover, the gear mechanism is preferably coupled to a drive axle of the motor vehicle in a torque-transmitting manner or the drive axle is likewise coupled to the gear mechanism of this type. The gear mechanism therefore becomes an interface, at which the power which is produced by the fuel cell and the braked drive axle is conducted in an optimum manner into the respectively required application. The gear mechanism can preferably also be coupled in a torque-transmitting manner to an air expander for discharging waste air under pressure from the fuel cell. In this way, the recuperation power which is supplied by an air expander of this type from the waste air of the fuel cell can also be utilized in a use-related manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.